1. Field of the Invention
The invention relates to a technique for identifying and processing arriving channels from multiple points individually in an integrated services digital network.
2. Description of the Related Art
With the recent spread of integrated services digital networks (ISDNs), center services, such as multipoint television conferencing, multipoint voice graphic conferencing, and the like, are being implemented.
In order to implement these various services, the communications capacity is required to be several times the capacity of the basic channel (B channel) of the current integrated services digital networks. For these services, therefore, a plurality of basic channels on a line are used simultaneously.
When the connection is set up between communications terminals that provide various services and a multipoint central unit, the central unit is required to identify arriving channels from a plurality of points individually in an efficient manner for subsequent processing.
As a first prior art to implement such a function, there is a technique in which, when each terminal makes a request for connection to the central unit, it informs the central unit of its terminal number using the B channel after the connection has been established by the central unit.
With this prior art, however, actual communications commence after each communications terminal (terminal number) has been identified using control communications data on the B channel. The problem with the first prior art is therefore that it takes long time to the commencement of communications. In addition, each terminal is required to have a function of sending its own terminal number as control communications data over the B channel and the central unit is also required to have a function of receiving and identifying control communications data on each B channel. This makes the system configuration complex.
As a second prior art, a central unit is provided with lines, the number of which corresponds to the maximum number of communications terminals. Each terminal is allocated an individual line number and makes transmissions using the line allocated to it. The central unit recognizes a plurality of arriving channels originating on each line as incoming channels from the communications terminal corresponding to that line.
The problem with the second prior art is that the central unit has to be provided with lines, the number of which corresponds to the maximum number of communications terminals.